There are some differences between the far field and near field patterns of wide aperture antennas. The radio wave is also dependent on conditions such as the permittivity of the ground in the antenna circumference. For this reason, some differences may occur in the radio wave characteristics at the near field monitor compared to the far field signal. Improvement in estimation accuracy of far field characteristics by the near field monitor is useful for instrument landing systems (ILS), in which high integrity is required.